Quote:
Originally Posted by Frank Lee
The very act of creating lift, creates drag.
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The "perfect" teardrop shape creates lift at the top rear edge. It also creates downforce on the bottom rear edge, lift on the bottom front edge, and so on, so it balances. The point is that a shape that is meant to reduce drag can also create lift. A brick has no lift, no downforce, and a lot of drag. Would you rather have the teardrop or the brick?
The design of a car is constrained by the fact that it moves along on the ground. So most of the rear is always going to be slanted downward to minimize drag, and that surface is always going to create lift.
You can counteract that force with a "diffuser" which also reduces drag, and also creates downforce because of its angle.
Draw yourself a vector diagram.